1. Field of the Invention
The invention relates generally to emergency exit devices and more particularly to an emergency exit device for unlocking a door for an emergency using either a push bar or a remotely actuated solenoid and maintaining the unlocked condition with a mechanical hold off lock that is accessible from the emergency use side.
2. Description of the Prior Art
Emergency exit devices are well-known for locking a door while allowing a person to unlock the door in order to exit a building in an emergency. Such devices are necessary, for example, when a door should normally remain locked but must be available as an exit in case of a fire. In some installations the emergency exit device is also required to have a hold off lock that is accessible from the emergency use side of the associated door in order to retain the door in an unlocked condition.
A type of emergency exit device, termed a rim-type, mounts horizontally on one side of the door for locking the door while enabling a person on the same side to unlock the door by pushing on a push bar. Manually operated rim-type emergency exit devices have been in use for many years. However, these devices were limited by not being controllable from a remote location such as a security office. An early approach to solving the problem of remote control involved electrifying the emergency exit device with the use of a motor driven worm gear. However, the high cost, great weight, large power consumption, and the slow speed of the worm gear limited the desirability of this solution. Another example of an electrified rim-type emergency exit device is disclosed by Zawadzki in U.S. Pat. No. 3,767,238. Zawadzki teaches the use of a series of linkages driven by a spring and culminating in latch bolt that projects for locking a door. For remote control Zawadzki uses two solenoids, a hefty solenoid for counteracting the spring and pulling the linkages for retracting of the latch bolt and a smaller solenoid for tripping one of the linkages so that the latch bolt again projects. A similar electrified emergency exit device disclosed in U.S. Pat. No. 3,854,763 by Zawadzki et al. uses only one hefty solenoid for pulling the linkages and dispenses with the second smaller solenoid. The device disclosed in U.S. Pat. No. 3,854,763 also includes a manually operated dogging lock that is accessible from the emergency use side and operates on the solenoid armature for holding the linkages for retaining the bolt latch in the retracted position. Unfortunately, both of these electrified emergency exit devices are heavy and costly and require a large solenoid using a relatively large amount of electrical power to overcome the spring force and the friction and inertia due to the relatively heavy weight and complexity of the linkages that must be pulled.
Another example of a rim-type emergency exit device is disclosed in U.S. Pat. No. 4,458,928 by Hirschbein as a "Rim Type Panic Actuator" and incorporated herein by reference. The device described by Hirschbein shows a series of linkages for engaging or disengaging a star wheel that latches to a bar-type strike mounted on an associated door frame. A spring biases the linkages to a normal lock condition by engaging the star wheel to prevent it from turning. For an emergency use, the bias of the spring may be overcome by pushing against a spring-loaded push bar that is coupled for disengaging the sliding catch from the star wheel, thereby unlocking the door. An mechanical hold off lock is available from the emergency use side for dogging the linkages for maintaining the disengaged condition. The device using the star wheel door latch disclosed by Hirschbein is relatively simple, low cost, and light in weight. Unfortunately, it is limited by having no provision for remote access for unlocking the door. Presumably, to address this limitation an electrified emergency exit device using a solenoid was developed and sold under model names 3700EL/8700EL/8800EL by Adams Rite Manufacturing Company. Remote access to this device is provided by electrical wiring to the solenoid. When operated by an electrical current, the solenoid operates through a linkage to overcome the bias of the spring to disengage the star wheel for unlocking the door. Unfortunately, due to the linkage and the strength of the spring, the solenoid must be relatively large requiring special machining operations and needs a relatively high electrical current for actuation, thereby requiring heavier wires or a shorter distance to the remote access site. The EL models may be held in the unlocked condition with a lock. However, this lock is accessed through the door from the other side of the door and is not accessible from the emergency use side. Alternatively, a continuous current to the solenoid can be used to maintain the unlocked condition. Unfortunately, the owners of some installations consider the use of a continuous current wasteful and/or unreliable for simply maintaining an unlocked condition.